Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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Synchronization Behavior During Graceful Restart
LDP-IGP synchronization does not take place while the IGP is in the process of a graceful
restart. When the graceful restart completes, links for which synchronization has been
configured are advertised with maximum metrics in either of the following cases:
• LDP is not yet operational on the link and no holddown timer has been configured.
• The configured holddown timer has not expired.
During LDP graceful restart, no synchronization operations are done. If the LDP graceful
restart is terminated, LDP notifies the IGPs to advertise the links with the maximum
metric.
Synchronization Behavior on LAN Interfaces
LDP-IGP synchronization does not take place on LAN interfaces unless the IGP has a
point-to-point connection over the LAN configured on the interface. The reason for this
is that multiple LDP peers might be connected on such an interface unless a point-to-point
connection to a single peer has been configured. Because synchronization raises the cost
on the interface high enough to prevent traffic being forwarded to that link, if multiple
peers are connected, the cost is raised on all the peers even though LDP might be
unsynchronized with only one of the peers. Consequently, traffic is diverted away from
all the peers, an undesirable situation.
Synchronization Behavior on IGP Passive Interfaces
On IGP passive interfaces, the link cost is not raised when LDP-IGP synchronization is
configured and a triggering event occurs.
Synchronization and TE Metrics
When traffic engineering is configured for an IGP, LDP-IGP synchronization does not
affect the traffic engineering metric advertised for the link, regardless of whether the TE
metric is explicitly configured or the default value.
Related Topics Configuring LDP-IGP Synchronization on page 291
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Use of RSVP-TE Hello Messages to Determine Peer Reachability
RSVP-TE hello messages enable the router to detect when an RSVP-TE peer is no longer
reachable. When the router makes this determination, all LSPs that traverse that neighbor
are torn down. Hello messages are optional and can be ignored safely by peers that are
not configured to use the feature.
When you enable the hello feature on a virtual router or interface configured with
RSVP-TE, that RSVP-TE node periodically sends a unicast hello message to each neighbor
with which the node has established an LSP. The exchange of hello messages between
the peers establishes a hello adjacency. You can configure the hello interval to establish
how frequently the node sends hello messages. Hello messages are exchanged when
an LSP is set up and are stopped when the last LSP between the two peers goes away.
Copyright © 2010, Juniper Networks, Inc. 260
JunosE 11.2.x BGP and MPLS Configuration Guide